It is common in the prior art to employ filtering devices adapted to filter fine particulates from the fluid medium circulating through the system and constitute a primary filtering system for fluid recycled through the circuitry. Such filters are of relatively large capacity to be capable of handling the necessary flow volumes without becoming too quickly saturated with the collected contaminants to avoid the necessity of frequent replacement. Further such primary filters are disposed upstream of the fluid control circuitry and are typically associated with the outlet flow from the source of fluid supply and/or the return flow to the fluid reservoir.
It is also known in the prior art that filter devices can be constructed using a wire coil wound about a threaded body provided with slots to create openings of predetermined size. These openings form passageways between the exterior of the coil and an internal axial passage or passages formed in the threaded body. However, these prior art teachings are concerned primarily with forming a relatively fine primary filter and utilize a relatively complex construction involving several parts to assure the openings between turns of the coil are maintained within a small tolerance. Others deal with matching certain configurations of a wire coil to the threads on the body to form a highly refined, primary filter.
Examples of these prior art teachings include U.S. Pat. No. 4,569,763 which teaches a method to lock the ends of the wire coil to a threaded body but does not teach or address any other aspects of making use of such a device in connection with other fluid operative elements.
U.S. Pat. No. 5,028,008 discloses a device including a wire coil wound around a multiple port core which comprises a cylindrical body provided with a separate obstructing cover at one end and a separate base at the other end forming an outlet for fluid passing between the wire coil and interior passageways in the body.
However, the prior art has failed to provide a low cost device which addresses the problem of adequately shielding an orifice restriction in a fluid circuit in a practical manner which can be simply and inexpensively made using conventional methods and means.